Method of and means for forming unbreakable lenses



July 18 1939 E. G. I LoYD' 2,166,215

METHOD CF AND MEANS FOR FORMIIGv UNBREAKABLE LENSES Filed Dec. 2'8 19:56

ERT

Patented July 18, 1939 lPATENT OFFICE llIETHOD OF AND MEANS FOR FORMING UNBREAKABLE LENSES Ernest G. Lloyd, Los Angeles, Calif.

Application December 28, 1936, Serial No. 117,858

10 Claims.

This invention relates generally to eyeglass r spectacle lenses, and more particularly to formation of such lenses from non-breakable material.

The general object of the present invention ls to provide unbreakable eyeglass lenses, while a more particular object is to provide a method of and means for forming true dioptric curves on opposite surfaces of a suitable transparent, plastic material, which is substantially unbreakable when shaped in eyeglass lens form.

In accordance with the present inv-ention, the lenses are formed from blanks of a transparent plastic material, capable of being shaped under heat and pressure. I have found that an organic resin, a typical form of which is commercially available under the trade name Plexiglas, and which is in substance a polymerized derivative of acrylic acid, is particularly well adapted to the purpose of the present invention, having the physical and optical characteristics desired in a spectacle lens of the character wanted,

as well as being capable of being worked or formed in accordance with the method of the present invention.

The specific material named, when formed into a piece of the thickness of an ordinary eyeglass lens, is for all practical purposes entirely unbreakable. It is highly transparent, its light transmission being nearly 95%. The index of refraction of the material is 1.4975, thus differing but little from the index for optical glass. The material becomes suiciently plastic to be worked or bent at approximately 90 C.

In forming a spectacle lens from this material in accordance with my improved and preferred technique, I rst prepare a pair of dies, ground and figured with dioptric surfaces, which are identical, except for being of reverse curvatures, to those wanted on opposite sides of the finished lens. These dies must be of a material which-is both hard and capable of being given an optically smooth dioptric'surface, and I have found that dies formed of glass are suitable to the process. If material other than glass is used for these dies, as for instance an alloy such as stellite, its hardness must be equal to or greater than 68 on the Rockwell C scale in order to insure good results.

50 In calculating the curvatures of these surfaces, suitable account is of course taken of the fact that the refractive index of the material to be utilized differs slightly from that of glass. 'Ihese dioptric surfaces are thus ground on opposing sur- 55 faces of a pair of dies, typically of glass, or other suitable material, and this grinding operation may be done in the same general manner in which conventional eyeglass lenses are ground.

Having the two dies, formed of glass or other 60 material of like characteristics, a sheet or blank of the material of which the lens is to be formed .is placed therebetween, and the dies and material are then gradually heated up to from say 300 to 350 F. At the same time pressure is applied to the dies, which gradually increases as the temperature rises. the temperature of the material reaches approximately 300 F., the material becomes plastic and is formed, under the pressure exerted, to the curvatures of the dioptric surfaces on the dies. The pressure is then sustained, or preferably somewhat increased, while the temperature of the material is gradually decreased to approximately 100 F. At this time the pressure may be released and the lens removed from between the dies. Finally, after being taken from the dies, the lens is preferably hardened by suddenly cooling it to say -100 F. by placing it in an atmosphere of a very cold inert gas. This may easily be done by placing the lens in the gas rising from solid carbon dioxide. Any other cooled inert gas, as nitrogen, helium, argon, krypton, or neon, might be used in this step. Themcluri/ aturgesmgf the dies are transferred prefectly to the lens, Which"'c"omes "out with optically smoothsurfaces, and which isfree fiom""int'ernal stresses which mightotherwise tend subsequently to deform the lens.

Theinvent'ion will be better understood by referring now to the following detailed description thereof, reference being made to the accompanying drawing, in which:

Fig. 1 is a side elevation of a pair of die holders in accordance with the present invention;-

Fig. 2 is a section taken on line 2--2 of Fig. 1;

Fig. 3 is a view taken on line 3 3 of Fig. 2; Fig. 4 is a section taken on line 4-4 of Fig. 2; Fig. 5 is an elevation of a finished lens;

Fig. 6 is a section on line 6 6 of Fig. 5; and Fig. 7 is a diagram showing the relation between heat and pressure during forming of the lens.

In accordance with the preferred practice of my invention, the lens is formed between two die members I2 and I3, preferably of glass or siiilar hard smooth surfaced material which canI be formed with optically perfect dioptric curves. Whether of glass or other material, the hardness of" these dies should equal substantially 68 or greater on the Rockwell C scale to insure good results. As here shown, these dies I2 and I3 are square in outline, though this is of course not essential. Opposing surfaces I2a and |30. of the two dies are ground with the dioptric surfaces which are desired to be imparted to the surfaces of the lens to be formed, and this may be done by any well known grinding method such as is ordinarily used in grinding an ordinary glass lens. Each die block is made from a block of uniform thickness, which may typically be one half inch. One block is hollowed out, or given a concave shape, and` the edge thickness of this block remains substantially one half inch. The other block is ground down at the edges, or given a convex shape, and the center thickness of this block remains substantially one half inch. This holds true regardless of the specific curvatures given to the ground surfaces. Thus, for al1 curvatures, the sum of the edge thickness dimension" of one die and the center thickness dimension of the other die is a constant.

The flat outer surfaces I4 and I5 of dies I2 and I3 are backed up and supported by at surfaces l5 and Il, respectively, of a pair of die holders I8 and I9.

As here shown, die holders IS and I3 comprise metal, heat conductive blocks provided in their adjacent sides with square registering recesses 20, which are dened at the bottom by th'e aforementioned die engaging surfaces i6 and I7. Flange 2l around recess 2G in lower die holder I9 is cut away at the corners to provide for dowel pins 22 and perforated spacers 23 slidable on said dowels. For instance, as shown best in Fig. l, cach dowel pin E2 is screw-threaded at one end as at B, and is screwed into a screw-threaded socket in one die holder, while the other die holder is provided with a bore 25 adapted to receive and slide down over dowel pin 22 as the die holders are moved together. One dowcl pin is provided at each corner of the die holders, and the set of four dowel pins accurately guide the die holders to move toward one another in perfect alignment.

Spacers 23 are of such thickness that if there were no lens material between the dies, so that curved die surfaces I2a and i311. might contact one another, hen upon movement of the die holders together, the flange ZI of the upper die would engage the upper ends of said spacers simultaneously with engagement of upper die surface I4 by die holder surface IS. The die holders would then be in their extreme closed position, with no spacing provided for the lens. To establish the thickness of the lens to be formed, and to arrest movement o1 the die holders toward one another when the lens has been pressed to the thickness wanted, washers Sil of the exact lens thickness desired are placed on dowel pins 25 over spacers 23. Accordingly, assuming a lens blank of plastic lens material to be placed between the dies, the dies are pressed together until upper die holder I8 engages the upper surface of washers 30, thereby assuring that the lens L formed between the dies will be pressed to the exact thickness wanted. As shown in the drawing, a space is provided between the sides of the dies I2 and I3 and the inner surfaces 01"' the flanges 2l of the die holders.

The outer end of each die holder block is recessed, as at 313, to receive a pair of insulation plates and secured together as by screw 3?. Inner plate 35 supports an electric heating coil clement 39 in comparatively closeheating relation to the die holder wall portion l0 separating die receiving chamber 20 from heating coil recess 3G, said coll 39 radiating heat to wall portion lill to be conducted to the die within chamber 20. The ends of heating coil 39 are connected to terminal screws 2, which are in turn connected to connector pins C3 projecting from the side of the die holder between insulation plates 35 and 36, in the manner clearly illustrated in the drawings. These pins 13 are adapted to be plugged into a conventional electric socket supplied with a suitable source of electric current, as will be understood.

Secured to the outer ends of die holders I8 and I9, as by screws 45, are plates 46 which are connected by screws 'l and nuts 48. These screws simply hold the die holders in assembly, pressure being placed on the material between the .dies by pressing inwardly on plates 46, which is done in any suitable press, not necessary here to illustrate.

Assuming that the proper die blocks, of glass or other suitable material, have been provided and are in place in the die holders, with a lens blank of the plastic lens material therebetween, this blank being oi a size slightly larger all around than the dimensions ol the final lens, and being of uniform thickness and preferably, though not necessarily, initially substantially dat, the procedure of forming the lens is as follows: Connection is made between the two pairs of connector pins 63 and suitable electric supply current connector sockets, causing current to iiow through heating coils 39, whereupon die holders I8 and I9 and dies I2 and I3 gradually rise in temperature.

When the temperature of the dies has increased to approximately 300 F., or slightly higher, the lens blank between the dies is sufllciently plastic to be formed by the dies. As the temperature increases and reaches the value at which the material becomes plastic, pressure is gradually applied to the die holders by means of any suitable press, not shown. sure variations with time are approximately plotted in the graph of Fig. '7. It will be seen from this graph that the temperature of the material is raised from room temperature to approximately 300 F. (at which point the material is somewhat plastic) in approximately two minutes, and reaches its maximum temperature, approximately 350 F., in about ve minutes from starting time. At this time the electric heating current is disconnected and the dies and holders allowed to cool for approximately ten minutes, or until the temperature of the material has returned to approximately 100 F. The die holders are electrically heated as described within a suitable press, not shown, and during the heating process are subjected to pressure in accordance with the pressure curve of the graph of Fig. 7. As shown, until the temperature is sucient to render the material plastic in character, the pressure is kept comparatively low, being necesarily only sufficient to hold the parts in position. As the material reaches plastic temperature, however, the pressure is quickly increased to a cornparatively high value, for instance to a pressure of the order of 1,000 pounds per square inch.

Under this pressure the dies are pressed toward one another and bend and forni the plastic lens material into the exact shape and for1n-of the dioptric surfaces which have previously been ground thereon. The pressure at this time may be suiiicient to bring the upper die holder into engagement with spacer washers 30, and in this event such pressure is sustained during cooling of the material. Since the blank of thermoplastic orlgnally inserted between the dies was thicker than the final lens desired, the movement of the dies toward cach other and the pressure thus generated causes the plastic to flow outwardly between the die surl'aces. Alternatively. the pressure during this period ol" highest heat may be sufficient to transfer the dioptrc curves on the dies to opposite sides of the lens, but not quite such as to bring the upper die holder into engagement with spacer washers 30. In the latter' event, the pressure on the die holders The temperature and presis still further increased while the lens is cooling. This latter' procedure appears to have an effect beneficial to the perfection of the lens. The sustained or increased pressure during the cooling period sets the lens in the shape wanted and insures that when cooled and removed from between the dies, it will retain the exact shape which it was caused to assume while in a heated, plastic condition within the dies.

After being removed from the dies, the lens is preferably further hardened by sudden cooling. This is done in accordance with my invention by immersing the lens immediately that it is taken from the dies, at a temperature around 100 F. into a bath of very cold inert gas, thereby suddenly chilling the lens to a temperature of about 100 F. For instance, the lens may be placed in an atmosphere of carbon dioxide gas evaporating from solid carbon dioxide. Any other cooled inert gas may be used for this purpose. Lenses made in the manner described are found to possess a surfacewhich is harder than that of the original resin, particularly if the pressed lens is quickly chilled.

The cooled lens after .subjection to this treatment is entirely free from internal stresses such as might subsequently cause the lens to warp. The siufaces of the lens are optically true and smooth, and insofar as optical characteristics are concerned, the lens compares with a well ground glass lens. As previously stated, the lens is for all practical purposes entirely unbreakable. It is non-plastic at all ordinary temperatures, and when made of the specific material named above is free from discoloration or warping.

The process lends itself to production of bifc-cal as well as conventional lenses. In making a loi-focal lens, dies are used with the bi-focal curves established as desired, and such bi-focal surfaces are pressed in one operation on the lens blanks without any further alteration in the process. The lens illustrated in Figs. and 6 and the dies shown in Fig. 2, are of bi-focal type, as will be apparent from an inspection of those fig- It is to be understood that the disclosure of my invention as given above is simply illustrative and not limitative on my broad invention, and that various changes and modifications may be made without departing from the spirit and scope of my invention or of the appended claims.

claim:

1. A method of forming spectacle lenses which have a desired focal length, from an organic thermo-plastic material, which comprises: placing a solid blank of organic transparent thermo-plastic material of greater thickness than that desired in the finished lens between surfaces of opposing dies, said surfaces comprising the reverse of substantially optically perfect dioptric curves desired in the finished lens, said dies being so formed as to permit excess thermo-plastic material to ow out from between said dies; heating the dies and thermo-plastic material to a temperature at which the material becomes suihciently plastic to fiow only under pressure; moving one of said dies toward the other to press the thermo-plastic material with suihcient pressure to cause the material to conform to the contours of the die surfaces and to flow outwardly between the die surfaces; stopping the movement of the dies toward each other to obtain a lens of desired thickness and cooling the dies and material to a temperature below that at which it can be bent and worked while maintaining a pressure on the material, and then removing the formed material from between the dies.

2. A method of forming spectacle lens which have a desired focal length, from an organic, transparent thermo-plastic resin, which comprises: placing a solid blank of organic, transparent thermo-plastic resin of greater thickness than that desired in the finished lens between surfaces of opposing dies, said surfaces comprising the reverse of substantially optically perfect dioptric curves desired in the finished lens, said dies being so formed as to permit excess thermoplastic resin to flow out from between said dies; heating the dies and thermo-plastic resin to a temperature at which the resin becomes suinciently plastic to flow only under pressure, moving one of said dies toward the other to press the thermo-plastic resin with sufficient pressure to cause the resin to conform to the contours of the die surfaces and to flow outwardly between the die surfaces; stopping the movement of the dies toward each other to obtain a lens of desired thickness and cooling the dies and resin to a .temperature below that at which it can be bent and worked while maintaining a pressure on the k resin, and then removing the formed resin from between the dies.

3. A method of forming spectacle lenses which have a desired focal length, from an organic thermo-plastic material, which comprises: placing a solid blank of organic, transparent thermoplastic material composed of polymerized derivatives of acrylic acid of greater thickness than that desired in the finished lens between surfaces of opposing dies, said surfaces comprising the reverse of substantially optically perfect dioptric curves in the finished lens, one of said surfaces including bi-focal dioptric curves, said dies being so formed as to permit excess thermo-plastic material to ow out from between said dies; heating the dies and thermo-plastic material to a temperature at which the material becomes sufficiently plastic to flow only under pressure but not in excess of about 35G F., moving one of said dies toward the other to press the thermo-plastic material with sufcient pressure to cause the material to conform to the contours of the die surfaces and to flow outwardly between the die surfaces; stopping the movement of the dies toward each other to obtain a lons of desired thickness and cooling the dies and material to a temperature below that at which it can be bent and worked while maintaining a pressure on the material, and then removing the formed material from between the dies.

4. A method of forming spectacle lenses which have a desired focal length, from an organic thermo-plastic material, which comprises: placing a solid blank of organic, transparent thermoplastic material of greater thickness than that desired in the finished lens between surfaces of opposing dies, said surfaces being highly polished and of a hardness of at least about 68 on a Rockwell C scale, and comprising the reverse of substantially optically perfect dioptric curves desired in the finished lens, heating the dies and thermoplastic material to a temperature at which the material becomes sumciently plastic to flow only under pressure; moving one of said dies toward thev other to press the thermo-plastic material with sufficient pressure to cause the material to conform to the contours of the die surfaces and to ow outwardly between the die surfaces; stopping the movement of the dies toward each other to obtain a lens of desired thickness and cooling the dies and material to a temperature below that at Cil w iicli it can be bent arid worked while maintaining a pressure on the material, and then removing the formed material from between the dies.

5. A method of forming spectacle lenses which have a desired focal length, from an organic thermo-plastic material, w' ich comprises: placing a solid blank of organic, transparent therrnoiplastic material composed of polynierized derivatives of acrylic acid of greater thickness than that desired in the finished lens between surfaces of opposingr dies, said surfaces being highly polished and of hardness of atleast about 68 of a Rockwell C scale, and comprising the reverse of substantially optically perfect dioptric curves desired in the iiislied lens, one of said surfaces including bl-focal dioptric curves, said dies being so formed as to periiit excess thermo-plastic material to flow out from between said dies; heat-ing the dies and theriiid-plastic material to a temperature at which the material becomes sufficiently' plastic to flow only under pressure but not in excess of about 350 F.; moving one of said dies toward the other to press the thermo-plastic material with sufficient pressure to cause the material to conform to the contours of the die surfaces and to flow outwardly between the die surfaces; stopping the movement of the dies toward each other to obtain a lens of desired thickness and cooling the dies and material to a temperature below that at which it can be bent and worked while maintaining a pressure on the material, and then removing the formed matcrial from between the dies.

6. A method of forming spectacle lenses having a desired focal length from organic thermo-plastic material which comprises: placing a solid blank of organic, transparent thermo-plastic material of greater thickness than that desired in the finished lens between surfaces of opposing dies, said surfaces comprising the reverse of substantially opticaily perfect dioptric curves desired in the finished lens, said dies being so formed as to permit excess thermo-plastic material to flow out from between said dies, heating the ls "a'rf thermo-plastic material to a temperature at which the material becomes sufficiently plastic to flow only under pressure, moving one of said dies toward the other to press the thermo-plastic niaktei-.iai with sufficient pressure to cause the material to conform to the contours of the die surfaces and to ow outwardly between the die surfaces, coolu ing the dies and material to a temperature below that at which it can be worked while continuing to move the dies toward each other and finally stopping the movement of the dies to obtain a lens of desired thickness.

'7. A method of forming spectacle lenses and the like which have a desired focal length, from an organic thermoplastic material, which comprises: placing a solid blank of organic, transparent thermo-plastic materal composed of polymerized derivatives of acrylic acid of greater thickness than that desired in the finished lens,V

between surfaces of opposing dies, said surface. being highly polished, of a hardness of at least about 68 on a Rockwell C scale and comprising the reverse of substantially optically perfect dioptric curves desired in the finished lens, one of said surfaces including bi-focal dioplric curves, said dies being so formed as to permit excess thermo-plastic material to flow out from between said dies; heating the dies and thermo-plastic material to a temperature at which the material becomes suflciently plastic to flow only under pressuie but not in excess of about 350" F.; moving one of said dies toward the other to press the thermoplastic material with sufficient pressure to cause the material to conform to the contours of thc die surfaces and to ow outwardly between the die surfaces; stopping the movement of the dies towards each other to obtain a lens of desired thickness and cooling the dies and the material to a temperature below that at which it can be bent and worked while maintaining the pressure on the material and then removing the formed material from between the dies and subjecting it to the action of a cold inert gas.

8. A method of forming spectacle lenses and the like which have a desired focal length, from organic thermoplastic material, which comprises: placing a solid blank of organic transparent thermo-plastic material of greater thickness than that desired in the finished lens between surfaces of opposing dies, said surfaces comprising the reverse of substantially optical perfect dioptric curves desired in the finished lens, one of said surfaces including bi-focal dioptric curves, said dies being so formed as to permit excess thermoplastic material to flow out from between said dies; heating the dies and thermo-plastic matcrial to a temperature at which the material becomes sufficiently plastic to ow only under pres sure; moving one of said dies toward the other to press the thermo-plastic material with sufficient pressure to cause the material to conform to the contours of the die surfaces and to flow outwardly between the die surfaces; stopping the movement of the dies toward each other to obtain a lens of desired thickness and cooling the die: and material to a temperature below that at which it can be bent and worked while maintaining a pressure on the material, and then removing the formed material from between the dies.

9. In a machine for forming spectacle lenses and the like from organic thermo-plastic materials the combination of: a pair of die holders movable toward and away from each other; a pair of dies, each provided with a highly polished surface carrying a dioptric curve reverse of that desired on the finished lens, said dies being removably held by the die holders with the curved surfaces in opposing relation and adapted to act upon the thermo-plastic material inserted therebetween, said dies being smaller than said holders, to form a space around the sides of said dies, and removable stop means between said die holders and spaced from the sides of the dios for limiting the movement of the dies and holders toward one another.

10. In a machine for forming spectacle lenses and the like from organic thermo-plastic-materials, thc combination of: a pair of die holders movable toward and away from each other, each die holder including an opstanding flange; a pair of dies, each provided with a highly polished surface carrying a dloptric curve reverse to that desired on the finished lens, each of said dies being removably held within the upstanding iange of one of said holders but having its sides spaced from the flange; and removable stop means between opposing anges of said die holders and spaced from the sides of the dies for limiting the movement of the dies and holders toward one another.

ERNEST G. LLOYD. 

